This invention relates to a method for the dry molding of formed parts in automatic presses using powdered materials having a flowability characterized by a flow time of more than 60 seconds per 100 g of powder flowing from a 60.degree. standard funnel with a nozzle aperture of 4 mm and a nozzle length of 4 mm. The powder is conveyed into the mold of a press tool with a lower and an upper punch, by means of a filling device at a first operating position, is pressed in a separate second operating position, and at a separate third operating position, the finished molded parts are ejected. During an operating cycle the operation positions are successively assumed in stepwise fashion by the lower and the upper punch and the associated mold or die cavity containing the powder.
An important objective in the mass production of pressed powder parts in automatic presses is a small mass tolerance. For parts of a given size, the flow properties of a powder improve with decreasing tolerance. The flow properties are characterized by the time required for the powder to flow from a 60.degree. standard funnel with a nozzle aperture of 4 mm and a nozzle length of 4 mm. Customarily, the flow time is given in seconds per 100 g of powder. The flow properties of highly flowable powders are characterized by a flow time of approximately 20 seconds per 100 g of powder. Frequently, starting powders with poorer flow properties must also be processed in automatic presses. Such powders can be brought into a more flowable form by known granulating processes such as mechanical granulation, thermal granulation, and by granulating additives or by spray drying. Various powders have poor flowability and even after being subjected to the different granulating processes have flow properties of more than 60 seconds per 100 g of powder. The production of pressed (molded) bodies of material in powder form in automatic presses is described, for instance, in U.S. Pat. No. 4,080,128.
It is therefore an object of the invention to improve the known methods of producing molded bodies through the application of pressure so that it is possible to process materials in powder form such as metal powder, ceramic powders, metal oxide powders or mixed powders with different components, with a flow behavior of more than 60 seconds per 100 g of powder, in automatic presses, into molded parts with small weight or mass tolerances.